1. Field of the Invention
This invention relates to disk head assemblies for supporting read/write heads adjacent rotating disks in disk drives and more particularly, to a base plate for attaching a head suspension assembly to a head actuator arm.
2. Description of the Prior Art
In hard disk drives data are stored on magnetizable surfaces of a plurality of rotatable disks that are mounted in a coaxial stack on a housing of the drive. Transducer heads that write data to and read data from the disk surfaces are supported by an actuator that is mounted on the housing and can be actuated to position the transducer heads in alignment with concentric data tracks defined on the disks. Each transducer head is attached to one end of a head suspension that is connected to an actuator arm that extends from the actuator body. The suspensions include a flexible load beam constructed of light sheet steel that has a bend formed in it. The load beam acts as a spring that forces the head against the disk surface with an accurate pre-load or xe2x80x9cgram Loadxe2x80x9d. Air turbulence caused by the rotating disks lifts the heads slightly off of the disks so that the heads fly on an air bearing across the disk surfaces. The air bearing force is counteracted by the suspension gram load.
A head-carrying suspension is attached to an actuator arm using a base plate that forms a part of the head suspension. The base plate includes a flat flange portion and a cylindrical hub portion or boss. The base plate hub is passed through a load beam clearance hole and the flange is spot welded to the load beam. The combined base plate, load beam and a flexure make up a head suspension, and the suspension has the hub of the base plate extending through and beyond the load beam clearance hole.
The hubs of two suspensions are inserted into an actuator arm boss hole formed through an actuator arm extending from an actuator body, one hub entering an actuator arm boss hole from each end of the hole. In the prior art, a swage ball is passed through the cylindrical hubs to force the peripheries of the hubs to expand (swage) into tight engagement with the inner peripheries of the actuator arm boss hole. Thus, an actuator arm may carry two suspensions on opposite sides thereof to support two transducer heads in opposing directions, one up and one down.
Problems with this method of mounting transducer heads have arisen as the need for increased data storage capacity in hard disk drives has grown and/or the size of the disk drive has decreased to fit in small lap top computers. The problem of forming a strong connection between the actuator arms and the transducer suspensions has been made more difficult as the thickness of the components has become smaller.
A typical base plate has two primary regions, a flange region and a hub region. The flange region is a flat portion to which the load beam is welded. This area preferably remains flat and free from distortion so that it serves as a stable mounting feature for the load beam and ideally remains so throughout the swaging operation. The hub region is an extended boss whose upper end is contiguous with the flange portion and whose lower end passes through boss clearance holes in both the load beam and the actuator arm. The hub region supplies the retention torque between the base plate, which is welded to the load beam, and the actuator arm by plastically expanding and cold working during the swaging operation, creating a press fit with the actuator arm. A problem with this process is that the base plate flange becomes warped by stress from the hub during the swaging operation. Consequently, the load beam, which is welded to the base plate flange, is deformed by the warping of the base plate flange, adversely affecting the gram load on the transducer head.
U.S. Pat. No. 5,602,698 granted to Miyazaki, et al. on Feb. 11, 1997 there is provided an actuator arm assembly for a magnetic disk unit including a base and an actuator arm assembly rotatably mounted on the base. The actuator arm assembly has a first hole at one end thereof; a load beam supporting a magnetic head at one end thereof and a second hole at the other end. A spacer (base plate) is secured to the other end of the load beam and is fastened to the one end of the actuator arm. The spacer includes a flat portion, a cylindrical portion integral with the flat portion, and an annular groove formed between the cylindrical portion and the flat portion. A single or plurality of annular grooves may be formed in the flat portion of the spacer. In place of the annular groove or grooves, a plurality of linear grooves may be formed in the flat portion of the spacer. Additionally, the spacer includes a reinforcement rib formed on an outer periphery of the flat portion.
Cutting an annular groove or grooves in a base plate flange removes material and tends to weaken the flange. Thus the flange must be made thicker or ribs must be provided to reinforce the flange as shown in the Miyazaki, et al. patent. A disadvantage of this approach is that the ribs add to the overall thickness of the base plate which results in an increase in the overall height of a head stack assembly (HSA) in a fully assembled disk drive. This makes the prior art approach unacceptable in HSAs for note book sized computers. Also, since the annular or linear grooves tend to weaken the base plate, a thicker base plate is needed to overcome this effect, again making the prior art approach unacceptable in HSAs for note book sized computers. Additionally, it is expensive to make annular or linear grooves in a base plate.
It is an object of this invention to isolate the plastic flow of material in the hub region of the base plate from affecting the flange region and consequently reducing the amount of gram load change resulting from the swage process, without increasing the thickness of the flange.
Briefly, the invention is concerned with a base plate comprising a hub and a flange. The flange has an outer flange region at an outer periphery of the flange and a clamping region that surrounds and is contiguous with the hub. The flange has a strain isolation region that surrounds and is contiguous with the clamping region. The strain isolation region has a stress-reducing configuration that provides alternately patterned areas of continuity and areas of discontinuity between the strain isolation region and adjacent areas of the outer flange region and the clamping region.
In accordance with an aspect of the invention the discontinuity areas are slots and the continuity areas are spaces between the slots.
In accordance with an aspect of the invention the discontinuity areas are holes and the continuity areas are spaces between the holes.
The invention has the advantage that when swaging, the swage force and plastic flow in the hub region are isolated from the flange region.
An advantage of this invention is that a superior retention torque to swage force ratio is achieved with a lower gram load change.
An advantage of this invention is that the strain isolation region provides a region of strain isolation between the outer portion of the flange where the load beam is welded and the inner portion of the flange which is clamped fully thereby reducing outer flange deformation and gram load loss.